An inorganic/organic hybrid is advantageous in that superior flexibility, cotability and functionality of an organic substance and superior light transmittance, wear resistance, heat resistance and insulating property of an inorganic substance can be realized together, sintering is possible at low temperature, and processability is good. Accordingly, researches are actively carried out to put it into practical application for optical uses.
Conventionally, the inorganic/organic hybrid is prepared by a sol-gel method whereby a solution is prepared by hydrolysis and condensation of an organometal alkoxide using water and a catalyst, which is then cured. U.S. Pat. Nos. 6,054,253, 5,774,603 and 6,309,803 disclose applications of the inorganic/organic hybrid prepared by the sol-gel method to optical devices. However, the inorganic/organic hybrid prepared by the sol-gel method has silanol groups because the curing occurs insufficiently at low temperature. The remaining silanol groups cause a large transmission loss because they absorb light in the near infrared wavelength region at 1310 and 1550 nm. Moreover, when used for a long period of time, the silanol groups remaining inside the material may adsorb moisture in the air and thus degrade the device performance. U.S. Pat. No. 6,391,515 proposes a process for manufacturing a silica optical waveguide with silanol groups removed by preparing a solution of tetraethoxysilane via a sol-gel method and sufficiently curing by heating up to 800° C. after coating. However, this method is impractical because, unlike a pure inorganic material, when an inorganic/organic hybrid is cured at high temperature, organic groups inside the material is decomposed by heat.
Korean Patent Application Nos. 2001-23552 and 2002-23553 disclose application of an inorganic/organic hybrid prepared by the sol-gel method for a gate insulator of a TFT-LCD or a protective film for a color filter or a circuit. However, since the inorganic/organic hybrid is prepared by separately preparing an inorganic oxide sol and a polymeric organometal alkoxide and then mixing them, the risk of phase separation is high and it is difficult to attain uniform properties when applied for a large area. Further, since a large quantity of solvent is used, a problem may occur because of the evaporation of the solvent during drying. As a result, light transmittance may decrease. In addition, voltage resistance or wear resistance may be degraded since it is difficult to attain a dense structure because of poor dimensional stability.
In order to solve the aforesaid problem, Korean Patent Application No. 2004-25063 discloses a method of preparing an inorganic/organic hybrid for optical applications via a non-hydrolytic sol-gel method and then photocuring or thermally curing it using an initiator. In this method, the inorganic/organic hybrid typically has organic functional groups such as epoxy or acryl at its surface. However, since the organic functional groups have worse heat resistance, light resistance, or the like as compared to the bulk silica or silica-metal oxide composite, they result in decreased thermal stability of the inorganic/organic hybrid. Because of thermal degradation of the organic functional groups, the inorganic/organic hybrid experiences significant weight change at about 300° C. Hence, its application for optical materials requiring stability at high temperature is restricted. Further, the photocuring or thermal curing is problematic in that, since the curing is accomplished by a chain reaction initiated by the initiator, unwanted byproducts may be produced, which may degrade transparency, thermal stability, or the like. And, if the inorganic/organic hybrid has a large molecular weight, curing by the chain reaction may not occur sufficiently because of steric hindrance. As a result, thermal stability, hardness, or the like may be degraded.